Process for the treatment of hydrocarbons



June 5, 1945. w. A. scHULzE 2,377,580

PROCESS FOR TH TREATMENT 0F HYDRQCARBONS Filed Aug. 29, 1941 2 Sheets-Sheet l INVENTOR WALTER A. SCHULZE June 5, 1945. w. A. scHuLzE PROCESS FOR THE TREATMENT OF HYDROCARBONSv F11-ed Aug. 29, 1941 2 Sheets-Sheet 2 TORNE Patented June 5, 1945 PnooESs Foa THE'TREATMENT or" HYDaocAmsoNs a Walter A. Schulze, Bartlesville, 0kla., asslgnor to Phillips Petroleum Company, a corporation of Delaware Application August 29, 1941, Serial No. 408,876

(Cl. 26o-680) 2 Claims.

This invention relates to improvements in the catalytic dehydrogenation of hydrocarbons to produce oleiins and diolefins. It relates more particularly to an improved process'of producing butadiene by catalytic dehydrogenation of normal butane.

This is a continuation-impart of my co-pendilroapplication Serial No. 353,962, filed August 23,

In the production of the valuable diolefin butadiene from normal butane, Vtwo catalytic dehy drogenation reactions are involved; namely, the conversion of butane to mono-olenic butenes, and the conversion of butenes to the dioleiinic butadiene. These two reactions may be combined in asingle stage operation in which butane is` charged and butadiene extracted while a large volume of butane-butene recycle is handled. It is a disadvantage of this type of operation that the optimum conditions of temperature and pressure are quite diil'erent for the two reactions. Thus, in a process which depends on concurrence of the ,two reactions, a compromise on operating conditions is necessary whereby neither reaction is most eciently carried out.

When a two-stage catalytic dehydrogenation process is employed, butenes are produced in the first stage under conditions of temperature, pressure and reactant concentrations most suitable for their formation with a minimum of decomposition to undesired products. The butenes are then separated by suitable means `and subjected to a further dehydrogenation step with conditions carefully selected to allow the use of higher conversion temperatures along with higher concentrations of unsaturated hydrocarbons and the relatively unstable products. The dehydrogenation of butenes is accordingly carried out at low partial pressures of reactants and hence of diolelinie products to avoid excessive decomposition.

4One expedient for obtaining the Vnecessary low partial pressures of butenes during dehydrogena- 4 tion is the use of a suitable` inert diluent gas whereby the partial pressure of butenes may be varied with the total pressure of the dehydrogenation system. In this connection it has been found that the lower-boiling hydrocarbon gases are satisfactory diluents provided that said gases are `relatively easily separated from the C4 reactantsand products, and that the diluents are sutil.. ciently inert so `that dehydrogenation` of the diluent does not produce hydrogen in quantities large enough to affect the equilibrium in the dehydrogenation of `thekCr hydrocarbons.) Hydrocarbon fractions comprising propane have been found satisfactory in applications involving the dehydrogenation of butane, but the minor dehydrogenation of propane during the conversion of propane-butene mixtures at low partial pressures of said butenes has proved disadvan-tageous.

In'my zo-pending application serial No. 353,962 I have disclosed a method of operation in which the` predominantly unsaturated C3 fraction formed in the dehydrogenation of n-butane in the Vabsence of a diluent is separated with the butene-l pressure to the desired range, additional C3 material must be provided and a continuous recycle of the required volume maintained. This recycling of propane involves compression, fractionationl and storage facilities for the condensation, separation and return of the diluent to the second dehydrogenation step.

Thus, although the physical characteristics of C3 hydrocarbons are superior to those oi the other gaseous hydrocarbons for my purposes, the described use of propane-propylene mixtures alone as a diluent involves a large investment in expensive compression and/or cooling facilities for the condensation of the propane. The compression and cooling costs for the condensation of large volumes of propane at high pressures and/or low temperatures is an important item in plant equipment and operating costs.

I have now discovered a method of operation which retains the advantages of the Cs'hydrocarbon diluent as `produced in the iirst dehydrogenation stage and as separated with butene-l as the charge to the second dehydrogenationV stage. By -this method of operation the C3 hydrocarbon by-product is utilized to advantage, and a depropanizing fractionation on the products from the first dehydrogenation may be dispensed With-` In addition, my process may be operated so as to reduce greatly the volume of propane diluent circulated in the second dehydrogenation step or to eliminate completely. the propane recycling operation. This is accomplished in one embodiment of the present invention by adding tol the y factory yield of butenes per pass.

2 propylene-buteue-l 'char-ge sufficient water vapor to produce the desired butene partial pressure.

The reduction in the volume of propane handled and the use of the easily conden's'ible water vapor result in a drastic reduction in the compressor re.

erating ,cycles and greater economies'in plant equipment and operating costs than similar methods heretofore known. A further object is to utilize by-products from a first dehydrogenation stage as diluents in a second dehydrogenation stage. A

" still further object is to provide a, diluent comprising propylene and water for the dehydro- Ygenation of butenes whereby the production of butadiene therefrom is facilitated. I'hese and other objects of my invention will be evident from the following disclosure'.

I have-found that by operating an initial catalytic dehydrogenation step at low pressures to convert butane to butenes in the absence of any diluent a considerable quantity of Cs hydrocarbons occurs at conditions which afford a satis- This indicates that a number of reactions involving butane proceed according to the following equations:

tions are of greatest importance since they account for the formation of normal butenes (both isomers), and propylene. The first three reactions are so-called primary reactions while the Afourth is a secondary reaction dependent upon primary reaction products. Thus, propylene is present to a considerable degree in the efiiuents Whereas the secondary product, propane, is not given much chance to form and the amount is relatively small. While some propylene will be formed in practically all operations in which a satisfactory per pass yield of butene will be ob- `\tainecl from butane, it is preferable to utilize temperatures and catalysts of such nature that appreciable quantities of propylene will be formed `without substantially affecting the butene yield.

Such conditions of operation are hereinafter more fully described. In the event it. is desired to operate in' a manner which will result in little or no propylene formation, propylene from an outside source 'may be admixed with the diluent as described below for introduction into the second dehydrogenation stage.

If desired it will be possible to conduct the process in a' single stage', starting withV either butane or butene, and introducing a propylenecontaining Idiluent as described below into said single stage. When starting with butane for the production of butadiene, more severe catalytic vtreatment will be required. Y

The reactions illustrated by the nrst. two equaf1"- In treating an' effluent gas containing all the reaction products from the dehydrogenation of butane to segregate a suitable charge for a second catalytic dehydrogenation step, a gas containing compounds having the following boiling points must be processed with an initial separation as indicated.

This initial separation may be accomplished by compressing and cooling the vapors to condense the C3 and C4 hydrocarbons with a possible secondary recoverycperation to strip C3 hydrocarbons out of the uncondensed gases if desired. The required pressure will of course depend on the degree of cooling applied, and usually pressures of Z50-350 pounds gage are suicient. Some Cz hydrocarbons will remain in the liquid condensate, but the amount retained is not lharmful and may be reduced during subsequent fractionation of the condensate. g

By fractionationv of the condensate I obtain a satisfactory charge to the second dehydrogenation step of my process. This fractionation may be accomplished in one or in a sequence of co1- umns. In one case a highly eiiicient fractionating 'column is used to separate C3 hydrocarbons and butene-l overhead while the higher-boiling C4 hydrocarbons are the kettle product which I .recycle with fresh butane feed to the catalyst in my first step. The overhead product containing propylene,- propane and lbutene-l will have a composition approximating the following:

A (volume B (volume per cent) per cent) Propylene l5 20 Propaue. 2 4 Butene-l. 83 76 v-`Analysis A shows that under one set of condit'ions about 85 per cent of the C3 fraction is propylene, while the volume noted that by choosing even more severe conditions for the dehydrogenation of butane that a larger percentage of C3 hydrocarbons may be produced with satisfactory ratio of propylene to propane. In this case, I may produce in my rst dehydrogenation step a propylene-butene-l fraction containing about 25 per cent of C3 material of which the major portion is propylene as shown by analysis B above. Thus,`by proper regulation of operating conditions, a charge stock for the second stage dehydrogenation may be produced containing from about 10 to 30 per cent propylene.

The propylene-butene-l fraction is charged to the second dehydrogenation step for the conversion of butenes to butadiene. To the fresh feed -is added recycle butenes and sufficient water per cent of C3 hydrocarbons is 17 per cent of the total. I have also goes through line 25 to storage vessel 26.

butenes are returned to the catalyst. A frac--` tionating or stripping operation to remove Ca hydrocarbons may be included just prior to the butadiene extraction step.

The process may be more readily understood by reference to the accompanying drawing, which is a diagram of one form of apparatus in whic the invention may be practiced. l

In the flgurebutane enters the system through line I and is pumped by pump 2 and line 3 into heater 4 where the temperature is raised to the desired level. The heated vapors then pass through line 5 to catalyst cases 6 filled with a suitable dehydrogenation catalyst, The eiiluent vapors leave the cases through line 1 and enter heat exchange system 8 wherein they are cooled to the desired level. A portion of the effluent vapors may be returned to the charge line 3 ahead of the heater through line 'IA and a compressor (not shown).

Leaving the cooled vapors enter the compressing section I through line 9. This 'section comprises usually at least two stages of compression with compressors II and accumulators I2. r The liquid accumulator products pass through line I3 to the fractionating column I 4. 'I 'he uncondensed gas comprising hydrogen, C3 and lighter hydrocarbons, and other gases leave the accumulator by line I and pass to a vapor recovery plant I6. This plant may be of the oil absorption type and serves to recover C3 and heavier hydrocarbons yfrom the lighter gases. The recovered Ca and C4 material .is returned to fractionator I4 through line .11, while the light gases are removed by line I8. If desired, a small amount of the hydrogen-containing gas may be returned to the butane charge line through line Iii-A.

Fractionator I4 represents the fractionating equipment used to segregate the butene charge to the second dehydrogenation step. This may Abe operated to take overhead C3 hydrocarbons and the lowest boiling butene, namely, butene-1. 'I'he propylene-butene-l fraction passes through line I9, condenser 20 and into accumulator 2i, from which uncondensed gases pass by line 22 to the vapor recovery plant. A portion of the condensate is returned to the columns as reflux by pump 23 and line 24, while the excess liquid In this fractionation, the kettle product comprising butenes-2 and unconverted n-butane is taken through line 21 and .pump 28 and returned to the raw feed stream ahead of the heater.

The fresh butene charge from Vessel 26 'is fed through' line 29 and pump 30 to heater 3| together with recycle butenes from line 54 and suiiicient diluent to `produce a reduced butene partial pressure in the desired range. diluent comprises water vapor added through line 32 and C: hydrocarbons. The C3 hydrocarbon diluent which is predominantly propylene comprises that produced and separated in the This first dehydrogenation step plus varying amounts which may be added through line 58 from an external source indicated by line 6I) or from the de-propanizing column following the second dehydrogenation step through lines 4l` and 59. desired, small amounts of hydrogen-containing gases may be added through lines 44 and 59 to Iline 53.

The buten.A charge diluted with Ca `hydrocarbons and water vapor is heated in Cheater 3| to the required temperature and passes by line 33 to catalyst cases 34 filled with a suitable de# hydrogenation catalyst. The treated vapors leave the cases through line 35 and pass to cooling system 36 wherein the temperature is lowered suiiiciently to condense the water vapor, after which the cooled material passes through line 31 and the water is trapped out and removed from separator 38 by line 39. 'I'he hydrocarbon gases leaving separator 38 by line 40 are compressed in compressor 4I and pass through line 42 to-accumulator 43. The condensate from 43 comprising C3 and C4 hydrocarbons may` then pass through vline 45 to column 46 wherein C3 hydrocarbons may be separated as an overhead product. The uncondensed gas from accumulator 43 is taken through line 44 and may be vented from the system or passed through line 59 and processed in the vapor recovery plant IG or elsewhere along with the overhead product from column 4I; passing through line 41. The liquid product from the kettle of 46 is taken through line 48 with necessary cooling (not shown) to butadiene extraction unit 49 which may embody any of the known processes for extracting butadiene `from C4 hydrocarbon mixtures. The butadiene concentrate is removed by line 50 to storage vessel 5I. The hydrocarbons remaining after the extraction of butadiene are removed through line 52 and pump 53 which recycles the stream through line 54 to the catalytic treatment.

Alternately, the condensate from accumulator 43 may pass through line 55 to drying and refrigeration unit 56 and thence through line 51 to butadiene extractor 49 without intervening fractionation or stripping. lThe separation of Ca hydrocarbons may be accomplished by higher temperatures and/or lower pressures on accumulator 43 to a degree commensurate with satisfactory retention of C4 hydrocarbons.

In the first stage of my process pressures of l5 to 50 pounds gage are employed for the dehydrogenation of butane. Temperatures and pressures are selected within a range suitable for the catalyst used, and temperatures within the range of 1000 to 1200 F. are ordinarily employed. At these conditions flow rates of the order of 1 to 10 liquid volumes of butane per hour per volume of catalyst are usually maintained, although at the higher temperatures still higher flow rates may be used. Particular conditions of flow rates, temperature and pressure are usually chosen to conform to the characteristics of the specific catalyst employed.

The catalysts which are useful in the `first stage of my process are those having suitable activity in promoting the dehydrogenation of paraffin hydrocarbons at the preferred operating temperatures. These may include the natural and/or synthetic metal oxide catalysts either alone or mixed with each other or promoted by oxides of .metals of groups IV to VIII of the periodic system.

In the operation of the second dehydrogenaficienty C3 hydrocarbons and water vapor to maintain butene partial pressures within the.y

preferred range of 0.2 to one atmosphere. The volume of C: hydrocarbons included may vary rather widely from the minimum volume produced in the firstdehydrogenation step up to larger volumes provided by recycling C3 material from the secondvstage eiiluentsA or by addition from an external supply. In most cases, the volume of C3 hydrocarbons will be minor compared to the volume of water vapor, although this volume ratio' may be varied withspecic operations and within thev terms of this disclosure. In general, it is preferable that the total input to the second stage dehydrogenation should be over 50 per cent steam, and up to 65 per cent or higher is desirable. However, any appreciable amount of water vapor will contribute toward improved results to a certain extent, "and therefore practically any desired amount may be used, the proportions referred to l merely representing preferred conditions.

hydrocarbons with varying amounts of C: hydrocarbons according to the conditions of condensation. 'I'he uncondensed gases usually comprising C3 and lighter material having been separated, the condensate may then be fractionated for complete removal of C3 hydrocarbons, and the C4v liquid then treated for the extraction of butadiene. 'I'he unconverted C4 hydrocarbons are recycled to the catalyst and after steady-state conditions are established, a volume of C3 hydrocarbons approximately equal to the propylene and propane formed in the two stages of dehydrogenation is removed from the system at a point following the second catalytic treatment. f

An alternative feature of the second stage of lmy process is that the C4 condensate subsequent to at least a partial separation of C3 and lighter material as uncondensed gases may be dried and cooled to'suitable sub-atmospheric temperatures and treated directly for the extraction of butadiene. In this case, the de-propanizing step is eliminated, and the compression and condensation steps are operated so as to prevent any Substantial losses of C4 hydrocarbons-in the uncondensed gases. Any Cs hydrocarbons recycled with the unconverted butenes to the catalyst are not harmful as long as the propane concentration is .not allowed to pyramid.

tion step, the butene charge is diluted with sufpropane-propylene mixtures in the treated vapors in the presence of water vapor. In this manner, the propylene is most eciently utilized in its function of promoting the 'dehydrogenation of butenes and simultaneously suppressing the dehydrogenation of propane.

Ethane and lighter gases must be satisfactorily removed frcm the eiiluents of the first stage `in order to facilitate the segregation of the propylene-butene-l stock by fractionation. Compression of the vapors to fairly high pressures is one method of accomplishing this de-ethanizing step, but other variations of this method are possible. For example, refrigeration of the vapors prior to a low-temperature flashing operation at lower pressures to remove ethane and lighter material is possible. Fractionation of the condensate to separate propylene and butene-1 may be accomplished in a single column, or if desired the Ca hydrocarbons may be separated in one column and butene-1 in another column and the fractions combined ahead of the second dehydrogenation step.

The overhead fraction will contain minor amounts of dissolved light hydrocarbons, but these may be'retained as diluents. The other C4 hydrocarbons likely to be included' are isobutane and isobutene, but in the process described the amounts of these compounds formedare minor.

When other methods are used to segregate the i butene charge to the second stage, the Ca fraction may be separated in a. separate fractionation operation. For example, when the higher-boiling butenes-2 are being separated by a fractionation producing said butenes as a kettle product while butene-1 and n -butane are taken overhead and recycled to the \rst stage dehydrogenation, the Ca fraction is removed from the butene-l-n-butane fraction, usuallyfbefore thebutene.v separaunder the operating conditions described herein will ordinarily be approximately 20 per cent propylene and 80 per cent propane, with the actual.

values being dependent, of course, on the temperatures involved. However, when water vapor is used asthe major part of the diluent according to the present invention, a portion of the excess of propylene provided in the C: fraction from the first stage may survive the second dehydrogenation stage. Thus, it maybe desirable to recycle minor amounts of this C: fraction to the second stage until that concentration ofl C3 hydrocarbons is approached which will yield equilibrium tion, and is later `added to the butenes-2 charge to the second dehydrogenation. These and other modifications of the procedure for obtaining the butene stock for the second dehydrogenation will be apparent to those skilled in the art, and are applicable within the disclosure of the present invention.

The secondsta-ge of dehydrogenation is operated at partial pressures of butenes in the range of about 0.2 to oneatmosphere with total pressures usually between zero and 50 pounds gage. Low total pressures are desirable in order to operate with maximum volume concentrations of C4 material.

Higher temperatures are usually required in :the second-stage than in the first stage to obtain satisfactory yields of butadiene from ,butenes Thus, temperatures in the range of 11Go to l300 F. are ordinarily employed. Flow rates in the second stage are usually maintained between l and 10 liquid volumes of. charge per hour per volume of catalyst. The particular combination of flow rate, temperature and pressure for a specie operation will depend on the catalyst used and the degree ofconversion. A

The catalysts used in the second stage are those of satisfactory activity at the preferred temperature range which do not cause excessive decomposition products. -These may-include natural and/or synthetic metal oxide catalysts with or without promoting agents. 0f particular value are bauxite and'bauxite deactivated with barium hydroxide according to co-pending application Serial No.

353,961, filed August 23, 1940, of which I am a co-` inventor.

and/or polymerization of reactants orA In the catalytic dehydrogenation of butenes over the above-mentioned catalysts certain benefits have been noted from the use of water vapor as a diluent. Thus, while it has vbeen stated in the prior art that the presence of large quantities of water vaporwas detrimental to the activity of metal oxide dehydrogenation catalysts, this effect suppresses to some extent the poisoning of theA catalyst due to tar and/or coke deposition thereon, and that the catalyst activity is thus prolonged. Also, the dehydrogenation reaction is promoted to the extent that hydrogenation of the propylene occurs during the catalytic treatment.

Improved dehydrogenation by my process is noted even at temperatures in the highest portion of the dehydrogenation range. Thus at temperatures of 1220 to 1300 F. which give maximum conversion of butenes per pass, the decomposition of butenes to light gases and coke is decreased in the presence of the propylene-water vapor diluent and the ultimate yield of butadiene on the basis of the C4. charge is correspondingly improved. The effect of the combination propylene-water vapor dlluent in prolonging catalyst activity and permitting higher conversion per pass at higher temperatures is more pronounced than `would be expected from results obtained using either component separately. The proposed function of the propylene in suppressing the hydrogenation of the butenes is apparently complementary to the oxidative function of the water vapor in suppressing carbon deposition on the catalyst surfaces.

Butadiene separation may be carried out by any conventional method, such as chemical extraction by suitable solutions, such as vcuprous salt solutions, solvent extraction by sulfur dioxide and/or Steam two weight per cent of Ca hydrocarbons, almost exclusively propylene. A

The ellluents Were substantially de-ethanizedand then fractionated in a column operated so as to take butene-l and the C3 hydrocarbons overhead while butenes-2 and unconverted n-butane were taken from the bottom of the column and returned to the dehydrogenation catalystl along with fresh n-butane feed. When a constant recycle ratio was established, the per cent per pass conversion of n-butane produced about 13Y weight per cent of butene-l due to combined dehydrogenation of n-butane and isomerization of butenes-2 in the recycle stream. As the run progressed, catalyst activity was maintained by slowly increasing the conversion temperature up to about l150 F. at which point the run was discontinued for regeneration of the catalyst.

The propylene-butene-l product from the rst dehydrogenation was preheated and charged to the second stage combined with recycled C3 hydrocarbons and suflicient added water vapor to reduce the concentration of butene-l to about volume per cent. The charge was as follows:

Butene-l C3 hydrocarbons e The charge mixture was heated to 1l90 F. and i flow rate of 4 liquid volumes of charge per hour per volume of catalyst about per cent conversion of butenes per pass was obtained.

Conversion of butenes to butadiene amounted to about 50 per cent of the total conversion, with the rest being recovered as C3 and lighter gases. The eluents were-cooled to condense the water vapor and after the separation of the water, the

other solvents or other satisfactory physical extraction and/ or separation processes.

The butene stream which is recycled to the second catalytic treating section comprises the equilibrium mixture of the normal butenes, containing both butene-l and butene-2. This mixture, however, is also readily dehydrogenated to butadiene under essentially the same conditions as butene-l and is quite suitable for inclusion in the butene-l charge. Whenoperating with a nonhydrogenatable diluent, a small proportion ofA butane is also formed. However, with propylenelwdrocarbon gases `were compressed and cooled to condense the C4 components. About 45 volum per centv of the hydrocarbon gases was removed 4as Ca and lighter material, the balance corresponding to about volume per cent ofCl hydrocarbons or 80 weight per cent of the -butene charge was processed for the extraction of butadiene. The butadiene recovered corresponded to about 20 weight per cent of the butene charge and Normal butane was dehydrogenated over a cal- Y to about 25 per cent of the C4 condensate, the remaining per cent being recycled to the catalyst.

I claim:

1. In the conversion of butenes to butadiene the improvement comprising passing butenes into contact with a dehydrogenation catalyst under conditions suitable for dehydrogenation of butenes to butadiene, providing in the bute'ne feed such an amount of C3 hydrocarbon diluent, comprising propylene and propane that the ratio of i propylene to propane in the butene feed is substantially greater than the` corresponding equilibrium ratio prevailing under the dehydrogenation conditions, adm'xingwith the hydrocarbons a quantity of steam at least equal in volume to vthe volume of the hydrocarbon feed, separating butadiene from the ellluents of the dehydrogenation, and recycling unconverted butenes from the effluents of the dehydrogenation to the dehydrogenation catalyst as part of the butene feed.

2. In the conversion of butenes to butadiene the improvement comprising passing butenes into contact with a dehydrogenation catalyst at temper cent of ethane and lighter gases and about.

Volume per cent I quantity of steam atleast equal in volume to the volume of the hydrocarbon feed, separating bute.- diene lfrom the emuents ofthe 'dehydrogenatiom and recycling unconverted butenes from the eilluents of the dehydrogenation to the dehydrogenation catalyst as part of the butene feed.

WALTER A. SCHULZE. 

